Using pulse-width modulation (PWM) to control the rotation speed of a cooling fan is an established method for reducing the cost of a variable speed fan in a cooling system. PWM signals can vary the operating speeds of the cooling fan since the rotation speed of the fan is determined by the duty cycle. For example, a PWM signal having a duty cycle of 100 percent makes the fan run at maximum. Whereas, a PWM signal having a duty cycle of 50 percent makes the fan run at a rate approximately half speed.